Marathon electric water heaters have one-piece, blow-molded polybutene inner tanks that never leak and never rust. These inner tanks are wound with fiberglass for strength, insulated with spray foam that is completely free of CFC and HCFC ozone-depleting chemicals (typical heat loss is 5°F over 24 hours), and then covered with a hard polyethylene shell that won’t dent during shipping and after installation. In fact, Marathon claims that its manufacturing process yields a finished product that is 4 times more durable than a traditional steel water-heater tank.
Marathon water heaters do cost 2 to 3 times as much as a conventional steel heater of the same size, but they carry a no-leak lifetime warranty for as long as you own your home. If ownership is transferred, the coverage converts to a straight 15-year warranty, still longer than most of the competition. Tank sizes range from 15 gal. to 105 gal.